1. Field of the Invention
The present invention relates to an image processing apparatus, more particularly an image reading apparatus for reading by scanning an original image such as a positive or negative film or a picture with a linear image sensor.
2. Related Background Art
There are already known image reading apparatus for reading an original image with a line sensor such as CCD. In such apparatus the image reading magnification is varied, in the main scanning direction or the reading direction of the line sensor, by skipping or interpolation of the image data, and, in sub scanning direction perpendicular to the main scanning direction, by varying the advancing speed of the original image.
However, in an enlargement of the image, such method results in a deterioration of the image quality, since the resolving power becomes lower than that in real-size image reading. Also such method results in a change in the vertical-to-horizontal ratio of the read pixel, rendering the vertical-horizontal conversion, rotation, filtering etc. of the image more difficult. Also since the sub scanning is usually controlled by a stepping motor, the control of the sub scanning speed is relatively easy if the image reading magnification is represented by a ratio of integers but is very difficult if said magnification is an irrational number.